Study On Pulse Train Control Technique For Switching DC-DC Converters

Pulse train (PT) control technique, which realizes the output voltage regulation of switching DC-DC converters by applying two pre-set control pulses, high power control pulses and low power control pulses, with different discrete duty ratios, is a nonlinear and discrete control technique. Without error amplifier and its corresponding compensation circuits, PT controlled switching DC-DC converters are simple design and benefit with fast transient response. As an input-energy-based control, PT control technique is suitable for the converters which operate in discontinuous conduction mode (DCM).Up to now, the dynamics of PT controlled switching DC-DC converters have not been reported. Taking buck converter as an example, the discrete time model of PT controlled DCM buck converter is established in this thesis. Based on the model, dynamic behaviors, such as multi-periodicity behaviors and border collision bifurcation behaviors, of PT controlled DCM buck converter are revealed and studied. The effects of circuit parameters on the dynamics of PT controlled DCM buck converter are also analysised by using bifurcation diagrams and maximal Lyapunov exponent.In steady-state, PT controlled DCM switching DC-DC converter operates in multi-periodicity, i.e., μH high power control pulses and μL low power control pulses compose a control pulse repetition cycle. The combination of high and low power control pulses in the control pulse repetition cycle determines the control performances of PT controlled switching dc-dc converters, such as output voltage ripple and output voltage precision. However, control pulse combination analysis of PT controlled switching dc-dc converters have not been studied yet. Thus, steady state performance analysis of PT controlled switching dc-dc converters only focus on the output voltage variation in individual switching cycle. It is therefore necessary to study the combination of control pulses in one control pulse repetition cycle to investigate the control performances of PT controller. In this thesis, the control pulse combination of PT control technique is studied, some lemmas of control pulse combination rules are presented and the corresponding proofs of these lemmas are given.The control performances of PT controlled switching DC-DC converter operating under continuous conduction mode (CCM) is quite different to that under DCM. Low-frequency oscillation phenomenon which severely affects the steady-state and transient performances of PT controlled CCM switching converter. Previous literature has shown that low frequency oscillation is influenced by its equivalent series resistance (ESR) and can be avoided by choosing a correct ESR. However, high ESR within the capacitor increases the output voltage ripple, which is undesirable. With buck converter as an example, the discrete time model of PT controlled CCM buck converter is established. The effects of circuit parameters on the stability of PT controlled CCM buck converter are analysised. Then, valley current mode pulse train (VCM-PT) and peak capacitor current pulse train (PCC-PT) control techniques are proposed to eliminate low-frequency oscillation. Operation principles steady-state analysis and parameter design of VCM-PT and PCC-PT controlled buck converter are presented and compared with traditional PT controlled buck converter.Up to now, PT control technique is used in low power switching converter, to extend its application sphere, discrete phase shift (DPS) for phase shift full bridge (PSFB) DC-DC converter is proposed in this thesis. Compares with traditional PWM phase shift (PWM-PS) control technique, DPS control technique benefits from excellent transient performance.